A number of self-advancing mechanisms are used in the medical industry to advance instruments, such as an endoscope, internally of a patient's body.
Self-advancing endoscopes are disclosed in, for example, U.S. Pat. Nos. 4,934,786, 5,345,925 and 5,562,601. The devices disclosed in these patents all rely on the outer surface of the endoscope having a relatively movable portion that grips the internal wall of a passage through which the endoscope is passing. In that manner, the endoscopes rely on external pushing as their source of forward motion and the resultant construction of the mechanisms to achieve that motion can be relatively complex.
Another endoscope is disclosed in International Application No. PCT/AU99/00005, which is propelled forwardly by a piston slidably mounted within a tubular member of the endoscope. The piston is caused to move toward and impact on a distal end wall of the endoscope to provide forward motion. A wire or other mechanism is used to retract the piston for subsequent acceleration and impact with the end wall, in order to further advance the endoscope. A disadvantage of such an arrangement is that the impact of the piston can produce an uncomfortable sensation within the patient and the use of a retracting wire may complicate construction of the endoscope and compromise operating efficiency, such as due to frictional resistance between the tubular member and the wire.